FIG. 1 is a schematic diagram of exposure process of semitransparent mask with large area. As shown in FIG. 1, a surface of a substrate 1 facing to a mask 4 has different heights in different regions since there is metal wire 2; the surface becomes a flat surface after it is coated with photoresist 3, and the surface coated with the photoresist 3 has uniform distance from a substrate 5 of the mask 4. Since the surface of the substrate 1 facing to the mask has different heights in different regions, the photoresist 3 coating each region of the surface of the substrate 1 facing to the mask has different thickness. As shown in FIG. 1, H1 is a thickness of the photoresist 3 of semi-exposed region, H2 is the thickness of the photoresist 3 of semi-exposed region, H3 is the thickness of the photoresist 3 of unexposed region, wherein H2 is less than H1.
FIG. 2 is a distribution schematic diagram of photoresist of the developed substrate as shown in FIG. 1. As shown in FIG. 2, portions of the mask 4 opposite to the semi-exposed regions of the substrate 1 have same transmittance. After the photoresist 3 coated on the substrate 1 is exposed and developed, the photoresist 3 remained on the portion corresponding to H1 has a thickness of H11, the photoresist 3 remained on the portion corresponding to H2 has a thickness of H21; H31 is the thickness of the photoresist 3 of the unexposed region, wherein H21 is still less than H11.
In subsequent processes, an ashing process is needed to be performed to the photoresist 3 in H11 region and H21 region, thereby to etch these two regions.